Computer Fundamentals (Anita Goel)-51-100.pdf

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You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  The Computer System Hardware | 33 ® USB Ports— to connect newer peripherals like cameras, scanners and printers to the com puter. It uses a thin wire to connect to the devices, and m any devices can share that wire simultaneously. ® Firewire is another bus, used today m ostly for video cameras and external hard drives. © RJ45 connector (called LAN or Ethernet port) is used to connect the com puter to a netw ork. It corresponds to a netw ork card integrated into the m otherboard. © VGA connector for connecting a m onitor. T his connector interfaces with the built-in graphics card. ® Audio plugs (line-in, line-out and m icrophone), for connecting sound speakers and the m icro­ phone. T his connector interfaces w ith the built-in sound card. ® PS/2 port to connect mouse and keyboard into PC. © SCSI port for connecting the hard disk drives and netw ork connectors. 2.10.3 Expansion Slots T he expansion slots (Figure 2.17) are located on the motherboard. T he expansion cards are inserted in the expan­ sion slots. These cards give the com puter new features or increased performance. There are several types o f slots: © ISA (Industry Standard Architecture) slot— T o connect m odem and input devices. ® PC I (Peripheral C om ponent In te rc o n n e c t) slot— To connect audio, video and graphics. T hey are m uch faster than ISA cards. ) A G P (Accelerated G raphic Port) slot— A fast port for a graphics card. © PCI (Peripheral Component Interconnect) Express slot— Faster bus architecture than AGP and PCI buses. © PC Card— It is used in laptop computers. It includes Wi-Fi card, network card and external modem. Figure 2.17 Expansion slots 2.10.4 Ribbon Cables Ribbon cables (Figure 2.18) are flat, insulated and consist o f several tiny wires m oulded together that carry data to different com ponents on the m otherboard. T here is a wire for each bit o f the word or byte and additional wires to coordinate the activity o f moving inform ation. T hey also connect the floppy drives, disk drives and C D -R O M drives to the connectors in the m otherboard. Nowadays, Serial Advanced Technol­ ogy A ttachm ent (SATA) cables have replaced the ribbon cables to connect the drives to the m otherboard. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  Computer M em ory | 41 H igh H igh Low Figure 3.2 Memory hierarchy T h e internal m em ory and external m em ory are the two broad categories o f m em ory used in the com puter. T h e internal m em ory consists o f the C P U registers, cache m em ory and prim ary m emory. T h e internal m em ory is used by the C P U to perform the com puting tasks. T h e external m em ory is also called the secondary m emory. T h e secondary m em ory is used to store the large am o u n t of data and the software. In general, referring to the com puter m em ory usually means the internal memory. V _____ __ -........................................................................................................................................................... - V 0 Internal Memory— T h e key features o f internal m em ory are— (1) lim ited storage capacity, (2) tem porary storage, (3) fast access, and (4) high cost. Registers, cache memory, and primary' m em ory constitute the internal memory. T h e prim ary m em ory is further o f two kinds— RAM and R O M. Registers are the fastest and the m ost expensive am ong all the m em ory types. T h e registers are located inside the C P U , and are directly accessible by the C P U. T h e speed o f registers is between 1—2 ns (nanosecond). T h e sum o f the size o f registers is about 200B. Cachc m em ory is next in the hierarchy and is placed between the C P U and the main memory. T h e speed ol cache is between 2 -1 0 ns. The cache size varies between 32 KB to 4M B. Any program or data that has to be executed m ust be brought into RAM from the secondary memory. Prim ary m em ory is relatively slower than the cache memory. T he speed o f RAM is around 60ns. T h e RAM size varies from 512KB to 3GB. 0 Secondary M emory — T he key features o f secondary m em ory storage devices are— (1) very high storage capacity, (2) perm anent storage (non-volatile), unless erased by user, (3) relatively slower access, (4) stores data and instructions that are not currently being used by C P U b u t may be required later for processing, and (5) cheapest am ong all memory. T h e storage devices consist o f two parts— drive and device. For example, m agnetic rape drive and m agnetic tape, m agnetic disk drive and disk, and, optical disk drive and disk. T h e speed o f m agnetic disk is around 60m s. C o p y rig h te d m aterial You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  Computer M em ory | 45 ® T h e R O M m em ory chip (Figure 3.5) stores the Basic Input Output System (BIOS). BIOS provides the processor with the inform ation required to boot the system. It provides the system with the settings and resources that are available on the system. BIOS is a perm anent p art o f the com puter. It does n o t load from disk but instead is stored in a RO M m em ory chip. T h e program code in the BIOS differs from ordinary software since it acts as an integral part o f the com puter. W hen the com puter is turned on, the BIOS does the following things— CM OS battery ROM BIO S Figure 3.5 ROM BIOS and CMOS battery on a motherboard Power On Self Test (POST) is a program that runs autom atically when the system is booted. BIOS perform s the power-on self-test. It checks that the m ajor hardware com ponents are w orking properly. BIOS setup program , which is a built-in utility in BIOS, lets the user set the m any functions that control how the com puter works. BIOS displays the system settings and finds the bootable devices. It loads the interrupt handlers and device drivers. It also initializes the registers. Bootstrap Loader is a program whose purpose is to start the com puter software for operation when the power is turned on. It loads the operating system into RAM and launches it. It generally seeks the operating system on the hard disk. T he bootstrap loader resides in the R O M. T h e BIOS initi­ ates the bootstrap sequence. ® R O M s are o f different kinds. T hey have evolved from the fixed read only m em ory to the ones that can be program m ed and re-program m ed. T hey vary in the num ber o f re-writes and the m ethod used for the re-writing. Program m able R O M (PR O M ), Erasable Program m able R O M (EPR O M ) and Electrically Erasable Program m able R O M (EEPR O M ) are some o f the RO M s. All the differ­ en t kinds o f R O M retain their content w hen the power is turned off. PROM can be program m ed w ith a special tool, b u t after it has been program m ed the contents cannot be changed. PR O M m em ories have thousands o f fuses (or diodes). H igh voltage (12 V) is applied to the fuses to be burnt. T h e b u rn t fuses correspond to 0 and the others to 1. EPRO M can be program m ed in a sim ilar way as PR O M , b u t it can be erased by exposing it to ultra violet light and re-program m ed. E PR O M chips have to be removed from the com puter for re-writing. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  An. Computer M em ory | 49 Track sector sector Figure 3.10 Tracks and sectors of a disk 0 M agnetic disk is inserted into a m agnetic disk drive for access. T h e drive consists o f a read/write head that is attached to a disk arm, which moves the head. T h e disk arm can move inward and outw ard on the disk. 0 D uring reading or w riting to disk, the m otor o f disk drive moves the disk at high speed (6 0 -1 5 0 times/sec.) 0 Accessing data o n the disk requires the following— T h e read/w rite head is positioned to the desired track where the data is to be read from or w rit­ ten to. T h e tim e taken to move the read/write head to the desired track is called the seek time. O nce the read/w rite head is at the right track, then the head waits for right sector to com e under it (disk is m oving at high speed). T h e tim e taken for desired sector o f the track to com e under read/w rite head is called the latency time. O nce the read/w rite head is positioned at the right track and sector, the data has to be w ritten to disk or read from disk. T h e rate at w hich data is w ritten to disk or read from disk is called data transfer rate. T h e sum o f seek tim e, latency tim e and tim e for data transfer is the access tim e o f the disk. 0 T h e storage capacity o f disk drive is m easured in gigabytes (GB). © Large disk storage is created by stacking together m ultiple disks. A set o f same tracks o n all disks form s a cylinder. Each disk has its ow n read/w rite head which w ork in coordination. © A disk can also have tracks and sectors on both sides. Such a disk is called double-sided disk. T h e features o f m agnetic disk are— © C heap storage device © C an store a large am ount o f data © Easy to carry or transport © Suitable for frequently read/w rite data © Fast access device © M ore reliable storage device © To be prevented from dust, as the read/w rite head flies over the disk. Any dust particle in between can corrupt the disk. ______ 50 | Basics of Computer Finding data on a m agnetic disk is as follows— © In order to use a disk, it has to be form atted. Form atting includes assigning addresses to various locations on disk, assigning location o f root directory and checking for defects on the surface o f disk. © D uring form atting, the tracks and sectors o f a disk are labeled, which provides an address to each location o f the disk. © T here are different m ethods to form at a disk. File Allocation Table (FAT) is the com m only used logical form at for disk form atting perform ed by W indows. © Four areas are created when a disk is form atted using FAT— Boot Sector It contains the program that runs when the com puter is started. T h e program checks if the disk has files required to run the operating system. It then transfers control to an operating system program which continues the startup process. Boot sector also contains infor­ m ation about the disk, like num ber o f bytes per sector and n u m ber o f sectors per track. This inform ation is required by the operating system to access the data on the disk. File Allocation Table It records the location o f each file and status o f each sector. W hile read­ ing or w riting to disk, operating system checks the FAT to find free area o r locate where data is stored on disk, respectively. Root Directory T his is the m ain folder o f disk. It contains other folders in it, creating a hier­ archical system o f folders. T h e root directory contains inform ation about all folders on the disk. D ata Area T h e rem aining area o f the disk (after boot sector, FAT, root directory) is the data area. It stores the program files and data files that are stored on the disk. © T he W indow s XP and the W indow s 2000 operating system use the N ew Technology File System (N TFS) 5 file system. T h e N T F S 5 file system offers better security and increased perform ance. It allows using o f filenames that are more than eight characters long. © Floppy disk, hard disk and zip disk are the different types o f m agnetic disks. 3.10.1 Floppy Disk © Floppy disk (FD) is a flat, round, single disk m ade o f M ylar plastic and enclosed in square plastic jacket (Figure 3.11). © Floppy Disk Drive (F D D ) is the disk drive for floppy disk. © T h e floppy disk is inserted into the floppy disk drive to read or w rite data to it. © Floppy disk has a w rite-protcct slide tab that prevents a user from w riting to it. © A floppy disk may be single-sided or double-sided disk, i.e., data can be read and w ritten on one and both sides o f floppy disk, respectively. © T hey are portable. T hey can be removed from the disk drive, carried o r stored separately. © T h e y are small and inexpensive. © F lo p p y disks are slower to access than hard disk. They have less storage capacity and are less expensive than hard disk. © T h e y com e in two basic sizes— 5 -lA inch and 3 -Vi Figure 3.11 Floppy disk inch. C o p y rig h te d m aterial  Computer M em ory | 51 ® T h e 5 -V\ inch disk came around 1987. It can store 360 KB to 1.2 M B o f data. ® T h e 3-Vz inch disk has capacity o f 400 KB to 1.44 M B. It usually contains 40 tracks a n d 18 sectors per track and can store 512 bytes per sector. 3.10.2 Hard Disk ® A hard disk (H D ) consists o f one or m ore platters divided into concentric tracks a n d sectors. It is m o u n ted on a central spindle, like a stack. It can be read by a read/w rite head that pivots across the rotating disks. T h e data is stored on the platters covered w ith m agnetic coating (Figure 3.12). Spindle arms head Figure 3.12 Parts of hard disk ® H a rd disk is a fixed disk. T he disk is n o t removable from the drive, unlike floppy disk. ® T h e hard disk and H ard D isk Drive (H D D ) is a single unit. ® H ard disk can store m uch m ore data than floppy disk. T h e data in hard disk are packed m ore closely (because fast spinning uses smaller m agnetic charges) and they have m ultiple platters, w ith data being stored on b oth sides o f each platter. Large capacity hard disks m ay have 12 o r m ore platters. ® U nlike floppy disk, the read/w rite head o f hard disk does n o t touch the disk d u rin g accessing. ® H ard disk can spin at the speed o f up to 10,000 revolutions per m inute a n d have an access tim e o f 9 -1 4 ms. It stores 512 bytes per sector b u t the num ber o f sectors are m ore per track (54 o r more) than floppy disk. S Nowadays, hard disks are available that can store up to 500 G B o f data. Generally, PCs come with 160 GB hard disk. ® H ard disk is the key secondary storage device o f com puter. T h e operating system is stored o n the hard disk. T he perform ance o f com puter like speed o f com puter boot up, loading o f program s to C o p y rig h te d m aterial ________ 52 | Basics o f Computer prim ary m emory, loading o f large files like images, video, audio etc., is also dependent on the hard disk. 0 Nowadays, portable external hard disk drive is available which can be attached to the USB drive o f the com puter. T hey com e in the storage capacities o f 80 GB to 500 GB. 3.10.3 Zip Disk 0 T hey are high-capacity removable disk and drive. 0 T hey have the speed and capacity o f hard disk and portability o f floppy disk. 0 Z ip disk are o f the same size as floppy disk, i.e., 3 -Vi inch b u t have a m uch higher capacity than the floppy disk (Figure 3.13). 0 Z ip disk and drive were m ade by Iomega C orp. It comes as a com plete unit— disk, drive, connection cable, power cord and operating system. It can be connected to the com puter system externally using a parallel chord o r SCSI cable. 0 T h eir capacity ranges from 100 M B to 750 M B. T hey can be 3.13 Zip disk used to store large files, audio and video data. 3.11 OPTICAL DISK O ptical disk (Figure 3.14) is a flat and circular disk which is coated w ith reflective plastic m aterial that can be altered by laser light. O ptical disk does n o t use m agnetism. T h e bits 1 and 0 are stored as spots that are relatively bright and light, respectively. 0 An optical disk consists o f a single spiral track that starts from the edge to the centre o f disk. D ue to its spiral shape, it can access large am o u n t o f data sequentially, for example m usic and video. T he random access on optical disk is slower than that o f m agnetic disk, due to its spiral shape. 0 T h e tracks o n optical disk are further divided into sectors w hich are o f same length. T hus, the sectors near the centre o f disk w rap around the disk longer th an the sectors on the edges o f disk. Reading the disk thus requires spinning the disk foster w hen reading near the centre and slower w hen reading near the edge o f disk. O ptical disks are generally slower th an hard disks. Figure 3.15 shows the tracks and sectors in a m agnetic disk and optical disk. C o p y rig h te d m aterial  Computer Memory 1____ 5 3 Track (concentric circles) Spiral Sectors Sector wider track of same at edge than width center Magnetic disk Optical disk figure 3>15 Sectors and track in magnetic disk and optical disk ® O ptical disks can store large am o u n t o f data, up to 6 G B , in a small space. C om m only used optical disks store 6 0 0 -7 0 0 M B o f data. ® T h e access tim e for an optical disk ranges from 100 to 200 ms. ® T here are tw o m ost com m on categories o f optical disks— read-only optical disks and recordable optical disks. 3.11.1 CD-ROM ® Originally, C om pact D isk (C D ) was a popular m edium for storing music. Now, it is used in com ­ puters to store data and is called C om pact Disk-Read O n ly M em ory (C D -R O M ). ® As the nam e suggests, C D -R O M (Figure 3.16) is an optical disk th at can only be read and n o t w ritten on. C D -R O M is w ritten on by the m anufacturer o f the C D -R O M using the laser light. ® A C D -R O M drive reads data from the com pact disk. D ata is stored as pits (depressions) and lands (flat area) on C D -R O M disk. W hen the laser light is focused on the disk, the pits scatter the light (interpreted as 0) and the lands reflect the light to a sensor (interpreted as 1). ® As C D -R O M is read only, n o changes can be m ade into the data contained in it. ® Since there is n o head touching the disk, b u t a laser light, C D -R O M does n o t get w orn o u t easily. ® T h e storage density o f C D -R O M is very high and cost is low as compared to floppy disk and hard disk. ® Access tim e o f C D -R O M is less. C D -R O M drives can read data at 150Kbps. T h ey com e in m ul­ tiples o f this speed like— 2x, 4x, 52x, 75x, etc. ® It is a com m only used m edium for distributing software a n d large data. 3.11.2 DVD-ROM ® D igital Video Disk-Read O n ly M em ory (D V D -R O M ) is an optical storage device used to store digital video or com puter data (Figure 3.17). ® D V D s look like C D s, in shape a n d physical size. C o p y rig h te d m aterial You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  I — _ Com p u te r M e m o ry 1 57 user, have slow access, store the data and instruc­ digital camera, mobile phone, printer, laptop com­ tions that are not currently being used by C PU , and puter, and MP3 players. are cheapest among all memory. M agnetic disk and © Magnetic tapes are inexpensive, can store a large optical disk are storage devices. amount of data, are easy to transport, are slow access ® Organization o f memory with respect to the C PU , is device, and are suitable for back-up storage. as follows— registers are placed inside C PU , cache © Magnetic disks are cheap storage device, can store a memory is placed inside C PU , prim ary m em ory is large amount of data, are easy to carry, are suitable placed next in the hierarchy, and secondary memory for frequently read/write data and are fast access is the farthest from CPU. device. Access time o f disk is the sum o f seek time, 0 Registers are very high-speed storage areas located latency time and time for data transfer. inside the C PU. Registers are manipulated direcdy ® Floppy disk is a flat, round, single disk enclosed in a by the control unit o f the C PU during instruction jacket. It is portable, small, inexpensive and slower to execution. access than hard disk. It comes in two basic sizes— 0 Cache, the fast memory, is placed between the C P U 5-V4 inch and 3-V4 inch. and the RAM. T he contents from the RAM are ® Hard disk is a fixed disk and can store much more stored in the cache. data than floppy disk. Hard disk is the key secondary 0 RAM stores data and instructions during the storage device of computer. operation o f com puter. RAM is a random access © Zip disk have the speed and capacity of hard disk and volatile m em ory having lim ited size due to its portability of floppy disk. high cost. RAM affects the speed and pow er o f © Optical disk consists of a single spiral track that starts th e com puter. from the edge to the centre o f disk. It can store large © RAM memory chips are o f two types— D RAM and amount of data in small space. SRAM. DRAM is used as main m em ory as it is © CD-ROM is an optical disk that can only be read small and cheap. SRAM chip is used in cache m em ­ and not written on. It has high-storage density and is ory due to its high speed. a low-cost device compared to floppy disk and hard ® ROM is a non-volatile prim ary m em ory which stores disk. the data needed for the start up o f the computer. © DVD-ROM is a high-density optical storage device Instructions to initialize different devices attached which stores data on both sides o f the disk. It is used to com puter and the bootstrap loader are stored in to store a full-length movie. R O M. PRO M , EPRO M and EEPRO M are some 0 Recordable optical disks are CD-R, CD-RW and o f the ROM s. DVD-R. 0 Flash memory is a kind o f semiconductor-based non­ © Computer uses its memory from the time you switch volatile, rewritable com puter memory. It is used in on the computer till you switch it off. KEYWORDS Access time 40 Compact Disk - Read Only Digital Video Disk-Recordable Basic Input Output System Memory (CD-ROM) 53 (DVD-R) 55 (BIOS) 45 Compact Disk-Recordable Direct Access 46 Bit 40 (CD-R) 55 Dual Inline Memory Module Boot sector 50 Compact Disk-ReWritable (DIMM) 44 Bootstrap loader 45 (CD-RW) 55 Dynamic RAM (DRAM) 43 Byte 40 Complementary Metal-Oxide Electrically Erasable Programmable Cache Hit 42 Semiconductor (CMOS) 45 ROM (EEPROM) 45 Cache memory 42 Data Transfer Rate 49 Erasable Programmable ROM Cache Miss 42 Digital Video Disk-Read Only (EPROM) 45 Compact Disk (CD) 53 Memory (DVD-ROM) 53 File Allocation Table (FAT) 50 C o p y rig h te d m aterial You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book. You have either reached a page that is unavailable for viewing or reached your viewing limit for this book.  INPUT A N D DUTPUT DEVICES 0 Input-output unit— Input unit, output unit 0 Output devices— Hard copy devices, soft 0 Input devices— Human data entry devices, copy devices source data entry devices * 0 Hard copy devices 0 Human data entry devices ♦ Printer— Impact printers (dot matrix, Keyboard daisywheel, drum), non-impact printers Pointing devices— Mouse, trackball, (ink-jet, laser) joystick, digitizing tablet ♦ Plotter— Drum plotter, flatbed plotter Pick devices— Light pen, touch screen ♦ Computer output on microfilm 0 Source data entry devices (microfiche) Audio input device (microphone, sound 0 Soft copy devices— Monitor, visual display card, speech recognition) terminal, video output, audio response & * *.£ ' 5. Video input device (video camera, (speakers, headphone) *: : ?>'?! digital camera) 0 I/O port— Parallel port, serial port, USB Optical input devices— Scanner (hand port, firewire port ihvrf '4 A: